1. Field of the Invention
The invention relates to alkaline batteries and more particularly to the structure of the positive electrode of alkaline batteries.
2. Description of the Prior Art
Sealed alkaline batteries are of considerable importance as a source of energy. Their long shelf life, high efficiency, and reasonable charge and discharge rates make them highly desirable for many applications. Since the cell is sealed, little or no maintenance is required which for many applications is highly desirable. For example, sealed alkaline batteries are often used as a source of power in remote outdoor locations. Among alkaline batteries the nickel-cadmium battery is particularly noteworthy because of its exceptionally good performance. One of the particular problems associated with the use of alkaline cells connected in series is the accidental reversal of one or more of the alkaline cells. Reversal refers to the condition in which one or more cells becomes completely discharged while current generated from other cells connected in series is pumped through the discharged cell. This leads to the generation of hydrogen gas at the discharged positive electrode. Continued reversal of the cell may lead to extremely high pressures of hydrogen or oxygen which eventually results in the bursting or venting of the battery. This essentially destroys the battery and interrupts operation of the entire power package.
Both chemical and electronic procedures have been used to prevent the generation of hydrogen gas on battery reversal. In the chemical procedure a cadmium hydroxide is included in the positive electrode. On battery reversal the cadmium electrode is charged thus preventing an evolution of hydrogen gas. This procedure sometimes limits the life of the cell due to dendritic growth of cadmium which may electrically short out electrodes in the cell. Also this procedure reduces the capacity of the positive electrode.
Other procedures involve the use of various electronic circuits which sense the complete discharge of the cell and then by-pass that particular cell. Although these procedures are reasonably reliable, they all require voltages which reduce the voltage output of the cell.